Paramagnetic Resonance ofS-State Ions in Metals

The interaction between conduction electrons and paramagnetic ions in metals has been investigated by observation of the paramagnetic resonance of gadolinium in alloys and intermetallic compounds. Spectra of Gd in powdered samples were observed at temperatures between 1.4 and 500°K and frequencies between 10 and 80 kMc/sec. A single line has been observed with $g$ values varying between 2.01 and 1.88. A striking correlation has been established between the $g$ shifts and the susceptibility and the specific heat of the pure Rh-Pd and Pd-Ag alloys, leading to the conclusion that the shifts are due to the interaction of the host conduction electrons with the paramagnetic ions. Linewidth considerations indicate that this interaction is mostly of scalar form. From the observed dependence of the $g$ shift and linewidth on the magnetization we conclude that the interaction produces the electron Knight shift predicted by Yosida, rather than the shift predicted by Kittel and Mitchell. The observed negative shift indicates that there is a polarization of mostly negative sign in agreement with previous nuclear magnetic resonance observations on Gd${\mathrm{Al}}_2$ by Jaccarino et al. A possible mechanism for this negative polarization is the Anderson-Clogston mechanism. Some experiments on line broadening due to different magnetic species, and their connection to the absence of the $g$ shift of Gd and Mn in Ag are discussed briefly.